The invention is concerned with devices of the type described in U.S. patent application Ser. No. 497,979 filed May 25 1983 and assigned the same assignee as this application, and which has a published equivalent GB No. 2121507A. As is known per se, a device constructed in accordance with the present invention is composed of first and second components such as a ring and a shaft. These components rotate about a common axis and have confronting surfaces one of which is plain while the other is provided with a groove forming a raceway or track of at least part helical configuration. Balls are disposed between the confronting surfaces in mutual contact therewith under radial pre-load and the balls are guided for progressive continuous rolling movement along the track. The arrangement is such that direct linear motion between the components is resisted but linear motion of one component can be achieved by rotation of the other component. The balls are guided to transfer, parallel to the common rotational axis, between the start and end of the track.